1. Field of the Invention
The present invention relates generally to remote control of downhole tools through pressure change signals transmitted through a column of fluid in the well, and more particularly but not by way of limitation, to methods of programming the downhole tool.
2. Description of the Prior Art
Traditionally, downhole tools such as those utilized in drill stem testing of oil and gas wells have been controlled either by physical manipulation of the pipe string which carries the tools or by changing the pressure applied to a column of fluid standing in the well, with that pressure being directly mechanically applied to a power piston of the tool so as to move an operating element of the tool. This second mode of operation includes those tools which are directly operated by changing well annulus pressure which is communicated with a power piston of the tools, or so-called annulus pressure responsive tools.
More recently, the development of downhole tools including programmed electronic controllers has made possible the use of remote controlled tools which may receive command signals transmitted from a remote command station, located at the earth's surface, through any one of several means to a receiver contained in the tool. The programmed electronic controller then causes the operating element of the tool to be actuated through any one of several types of operating systems in response to the remotely received command signal.
One system which has been developed for remote communication with such a preprogrammed remote control downhole tool is the use of annulus pressure changes applied to a column of fluid standing in the well annulus to communicate with the downhole tool.
One very significant difficulty encountered with this communication technique is that the pressure change signal which is input to the column of fluid at the surface of the well is substantially distorted as it travels down through the column of fluid. Furthermore, the nature of the distortion can vary over time as the conditions within the well change over time.